The present invention relates to plastic dust-proof boots, wherein the boots are made of thermoplastic resin by means of blow molding and provided at least on one end of a bellows with a stationary ring to be fitted to an engaging groove formed on an attaching shaft. The boots are favorable particularly when the stationary ring is at the smaller diameter side.
The dust-proof boot may be used as dust covers for ball joints, steering rack boots to be used for automobiles, constantspeed joint boots and the like.
An example of a rack boot as shown in FIG. 1 will now be described. Such boots have been usually made of rubber such as chloroprene rubber (CR). However, from the viewpoint of molding workability and improvement of cold resistance mainly, molding of thermoplastic resin is studied and partly being used in practice. Such boots are manufactured by means of blow molding (particularly injection blow molding).
When boots are manufactured by means of blow molding, the stationary ring is pulled towards the bellows during the blow molding of the stationary ring at the side which connects to the bellows. Consequently, it is difficult to form the inner circumference base upright wall of the stationary ring in the boot at a nearly vertical state, i.e., sharply. Particularly, in the stationary ring at smaller diameter side, this tendency is significant on account of the small size. If the inner circumference base upright wall 2 of the stationary ring 1 is not formed sharply as shown in FIG. 2, when the stationary ring 1 is fitted to the engaging groove 5 of the attaching shaft 3, the locking action of the engaging groove 3 to the locking wall 5a is small and therefore the stationary ring 1 is apt to be pulled away. In order to prevent the stationary ring 1 from being pulled away, a rubber grommet 7 with a pullingproof flange 7a is interposed as shown in FIG. 3. However, sufficient pulling-proof property is not obtained in this method. Moreover, since the rubber grommet is used, the number of process steps which are needed for assembling the equipment as a whole is increased and snap action to enable easy confirmation of fitting to the engaging groove cannot be obtained.